Patent application title: Cooking Appliance
Wolfgang Thimm (Karlsruhe, DE)
E.g.o. Elektro-Gerätebau Gmbh (Oberderdingen, DE)
E.G.O. Elektro-Geratebau GmbH
E.G.O. ELEKTRO-GERÄTEBAU GMBH
IPC8 Class: AF24C1510FI
Class name: Stoves and furnaces stove lids and tops
Publication date: 2013-04-25
Patent application number: 20130098351
According to various embodiments, a cooking appliance having a cooktop
plate and a heating device which is arranged below the cooktop plate may
include an indicator device for optical temperature indication below the
cooktop plate. The indication devices may include a thermochrome material
for temperature indication wherein the thermochrome material essentially
consists of metal oxides, which are fluorescent for emitting light and
which are present in the manner of quantum dots having a predominant
proportion of grain sizes between 10 nm and 80 nm and which are admixed
in a fluorescent thermochrome paint.
1. A cooking appliance, comprising: a cooktop plate having a heating
device arranged underneath for heating a cooking vessel being positioned
above on said cooktop plate; and an optical indicator device for
temperature positioned below said cooktop plate, wherein said optical
indicator device comprises a thermochrome material for optical
indication, wherein said thermochrome material comprises metal oxides,
said metal oxides being fluorescent for emitting light and being present
as a powder with a major part of powder grains having a particle size
between 10 nm and 80 nm.
2. The cooking appliance of claim 1, wherein said major part of powder grains with said particle size is between 20 nm and 50 nm.
3. The cooking appliance of claim 1, wherein at least 50% of said thermochrome material has said particle size between 10 nm and 80 nm.
4. The cooking appliance of claim 3, wherein at least 75% of said thermochrome material has said particle size between 10 nm and 80 nm.
5. The cooking appliance of claim 1, wherein at least 90% of said thermochrome material having said small particle size are within a range of +/-10% of an average particle size.
6. The cooking appliance of claim 1, wherein said thermochrome material is based on cadmium (Cd).
7. The cooking appliance of claim 6, wherein said thermochrome material is CdSe (cadmium selenide).
8. The cooking appliance of claim 6, wherein said thermochrome material is CdS (cadmium sulphide).
9. The cooking appliance of claim 1, wherein said thermochrome material is arranged underneath said cooktop plate.
10. The cooking appliance of claim 9, wherein said cooktop plate is non-transparent but light-transmissive for a light wavelength of light emitted by the said thermochrome material.
11. The cooking appliance of claim 1, wherein said thermochrome material is applied on a carrier as a paint or a coating.
12. The cooking appliance of claim 11, wherein said carrier consists of an insulating material such as mica or ceramics.
13. The cooking appliance of claim 11, wherein said thermochrome material is present on a flexible adhesive label.
14. The cooking appliance of claim 1, wherein a change temperature for a color change of said thermochrome material lies in a temperature range of approximately 50.degree. C. to 90.degree. C.
15. The cooking appliance of claim 1, wherein a wavelength of said light emitted by said thermochrome material lies in a wavelength range of 480 nm to 650 nm.
16. The cooking appliance of claim 1, wherein said thermochrome material is arranged in a vicinity of one of said heating devices of said cooking appliance.
17. The cooking appliance of claim 16, wherein in a case of an induction heating device, said thermochrome material is arranged above said induction heating device.
18. The cooking appliance of claim 17, wherein said thermochrome material is arranged between said induction heating device and said cooktop plate.
19. The cooking appliance of claim 1, wherein said thermochrome material has physical properties of quantum points or quantum dots, respectively.
CROSS REFERENCE TO RELATED APPLICATIONS
 This application claims the benefit of German patent application DE 10 2011 085 112.7, filed on Oct. 24, 2011, the contents of which are incorporated by reference for all that it teaches.
 The disclosure relates to a cooking appliance including an optical temperature indicator. The optical temperature indicator may be particularly used as a heat indicator or residual heat indicator for a cooktop plate of the cooking appliance for protection against burning known per se.
 It is known from the German patent application DE 102011085117 to arrange thermochrome paint or thermochrome material on a carrier underneath a cooktop plate, for example on the upper side of an induction heating device which is pressed against the cooktop plate from below. A change temperature of the thermochrome paint is selected such that, for example, a clearly discernable color is visible as an optical indicator above a change temperature of the indicator that corresponds to a temperature at the cooktop plate that is regarded to be hazardous to the operator. Thus a warning signal is output to the operator. The warning signal disappears again when the temperature falls below said hazardous temperature at the cooktop plate. All in all, this way an optical indicator device for temperature or rather heat indication can be realized that works reliably and with sufficient precision and that does not require complex actuation or energy supply. However, for the reasons described in greater detail below, one cannot realize each and every practical use sufficiently well.
 The disclosure herein provides a cooking appliance as mentioned above with which problems with existing cooking appliances can be avoided and which particularly allows an advantageous optical temperature indicator, in particular as a heat indicator or residual heat indicator, which has a simple structure. According to various embodiments, a cooking appliance may include a cooktop plate with a heating device arranged underneath for heating a cooking vessel positioned on the cooktop plate. An optical indicator device for temperature may be positioned below the cooktop plate. This optical indicator device may include a thermochrome material for optical indication. The thermochrome material may include metal oxides being fluorescent for emitting light and being present as a powder with a major part of powder grains having a particle size between 10 nm and 80 nm.
 Said features and further features arise not only from the claims but also from the description and the drawings, wherein the individual features can be embodied in each case as one or more together in sub-combinations of an embodiment of the disclosure and in other fields and can be advantageous and capable of being protected on their own for which hereby protection is claimed. The division of the application into individual sections as well as cross headings does not limit the general validity of the contents thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
 Embodiments of the disclosure are schematically shown in the drawings and will subsequently be explained in more detail. The figures show in:
 FIG. 1 a sectional side view of a first cooking appliance according to the embodiments, having a ring-shaped optical indicator device with thermochrome paint around the heating device;
 FIG. 2 a second cooking appliance according to the embodiments having an induction coil as a heating device and an optical indicator device which is bonded face-to-face to the heating device;
 FIG. 3 an indicator device shown in a hot state of the cooktop plate or the optical indicator device according to FIG. 2;
 FIG. 4 a sectional view of the indicator device according to FIG. 2 on a much larger scale;
 FIG. 5 an extended 2-step indicator based on FIG. 3; and
 FIG. 6 an indicator yet once more extended similar to FIG. 3.
 As will be described in greater detail below with respect to the figures, the disclosure herein provides a cooking appliance with a cooktop plate having a heating device that is arranged underneath the cooktop plate. Thus, a cooking vessel including content positioned above the heating device on the cooktop plate can be heated. An optical indicator device for optical temperature indication is provided underneath the cooktop plate and is visible or discernable through the cooktop plate. The indicator device may include thermochrome material for the temperature indication.
 According to various embodiments, the thermochrome material may essentially include metal oxides that are fluorescent for emitting light and that are present as a powder. A major part of the powder or thermochrome material may have a particle size between 10 nm and 80 nm, particularly between 20 nm and 50 nm The powder or thermochrome material can be admixed in paint or coating which in turn is applied using a suitable method. The optical properties, also with regard to the fluorescence, after completion or finish are thereby largely determined by the admixed fluorescent thermochrome material.
 For the past 20 years, the physical properties of corresponding materials have been studied thoroughly in professional circles under the catchword "quantum point" or "quantum dot". In the same way, various production methods for such "quantum dots" or materials have been examined intensively, such as wet chemical or lithographical methods, for example.
 Thus, when reaching a change temperature, it is possible that the thermochrome material does not only change its color and along with that also slightly changes its visibility due to the changed shade of color per se, but said visibility is significantly changed or dramatically increased by the fact that the material is actually fluorescent and is above all selected such that above said change temperature it shows quasi immediate emission by itself, and thus is visible even through conventional cooktop plates of cooktops made from colored glass ceramics. For this reason, a very high perceptibility of the optical temperature indication is ensured in any case, particularly in the case of a high temperature lying above said change temperature where a warning should be output indeed. Thus, by means of the present disclosure, an optical indicator is created which comes closer to a conventional luminous display than obtainable by means of thermochrome indicator devices to date.
 Because of the small size or small grain size of the powder of the thermochrome material quantum effects or quantum properties of said materials can be used which cause the fluorescence of the thermochrome material. The powder grains of the material do no longer perform according to classical theory but as quantum particles with predefined energy gaps. They have an essential advantage to the effect that when excited with energy, they can emit light having a sharp wavelength, and thus they are visible. A narrow grain size distribution in said range is advantageous in this case.
 In an advantageous configuration of the embodiments, it is provided that at least 50% of the thermochrome material has a particle size in said range between 10 nm and 80 nm. In particular, at least 75%, preferably even more than 90%, that is to say the very predominant part is comprised therein. Even better effects can be achieved if said high proportion of the thermochrome material has particle sizes in the range of 20 nm to 50 nm, thus within an even smaller range.
 At least 90% of the thermochrome material with its small particle size can preferably be in a range of +/-10% of the average grain diameter. By means of such a narrow particle size distribution said effects can very well be generated or utilized.
 A multitude of materials that can exhibit fluorescent thermochrome effects can be considered as thermochrome materials. Advantageous materials are based on cadmium (Cd) such as CdSe (cadmium selenide) or CdS (cadmium sulphide).
 In an advantageous embodiment, in a way similar to the above mentioned German patent application DE 102011085117, it is possible to arrange the thermochrome material or the above mentioned paint or coating underneath the cooktop plate and to design the cooktop plate in a non-transparent manner. This does not mean that it should be impervious to light but merely that it does not have to be completely transparent. If, after all, the cooktop plate is transparent, naturally an indicator according to the disclosure works all the better. Thus the disclosed embodiments also work with a translucent cooktop plate. Naturally, a light transmission capability applies primarily to the light emitted by the fluorescent thermochrome material, and can thus also depend on light wavelengths.
 In another embodiment, the fluorescent thermochrome material can be applied on a carrier as a powder or as an admix to a paint or coating, particularly on an electrically and/or thermally insulating material of a carrier such as mica or ceramics. As an alternative, the thermochrome material can also be applied in a paint or coating on a carrier such as adhesive labels or foils, which on their part can be attached to various devices such as heating devices or induction coils or contact heating devices by simply sticking them on the latter.
 An application means of the thermochrome material can be designed as a face, a symbol, a letter or the like. It is also generally possible to use multiple thermochrome materials which can be arranged directly adjacent or even superimposed in a layer structure under certain circumstances. In this way, e.g., several change temperatures can be achieved for a quasi two-step indication process including differentiation of two temperatures. This would of course increase convenience of operation and convenience of indication even further.
 In yet another advantageous embodiments, the wavelength of the light emitted by the fluorescent thermochrome material is in the range of 480 nm to 650 nm. One the one hand, this light can easily be perceived by an operating person. On the other hand, it lies in a range of colors that are commonly used for coloring cooktop plates, which are often colored in a reddish-brown shade so that such an optical temperature indicator can be particularly well discerned through this type of cooktop plates as well.
 In yet other embodiments, an optical temperature indicator is designed in such a way that the fluorescent thermochrome material is arranged in the vicinity of a heating device of the cooking appliance. In a particularly advantageous configuration and in the case of an induction heating device, the thermochrome material is arranged above the induction heating device or interposed between the latter and the cooktop plate. It can, for instance, be designed as a coating or a colored adhesive label on an insulating cover of such an induction heating device.
 More advantageous than with a radiant heating device, the disclosure herein may be realized with a so-called keep-warm heating device, with the keep-warm heating device acting as contact heating element, and including electrical resistance heating elements and being arranged at the bottom side of the cooktop plate. Cooking vessels placed on top will then be kept warm together with their content at a temperature of 50° C. to 80° C. so that the food inside can be served at any time. Such keep-warm heating elements or the electrical resistance heating elements therein do by far not reach such high temperatures as radiant heating devices but can be kept within a temperature range that is better to handle and in which sufficiently strong materials are available. On their upper side, which can be a cover or a carrier for the resistance heating element, towards the cooktop plate, thermochrome material can be applied as otherwise also described, for instance as direct coating or as an adhesive label. The carrier for the resistance heating element can be made from ceramics, such as aluminium oxide or the like, or from a metal and an insulating layer.
 In the case of the above mentioned resistance heating devices or thick film heating devices, the electrically insulating carrier may be arranged between the heating resistor and the cooktop plate for safety reasons. Therefore a coating of the thermochrome material or the above-mentioned adhesive label or foil having a thermochrome material can be applied on the side of the carrier that abuts the bottom side of the cooktop plate.
 Turning now to the figures, FIG. 1 shows a sectional side view of a cooking appliance in the form of a cooktop 11 having a cooktop plate 13 with a heating device 18 which is arranged underneath said cooktop plate. The cooktop plate 13 can be a conventional glass-ceramic cooktop plate including a bottom side 14 and an upper side 15. It can advantageously be colored, for instance in reddish-brown or milky-white, as this is often the case. As an alternative, it can be essentially translucent or transparent, at least above the indicator device or the fluorescent thermochrome material, respectively. However, then the advantage of the fluorescent properties is less pronounced since transmission through the cooktop plate 13 is easier. The cooktop plate may be colored or coated or furnished with paint around the transparent areas in a kind of masking as known per se.
 Generally, the heating device 18 can be a radiant heating device used for cooktops 11 or a keep-warm heating device or a contact heating device on the one hand or an induction coil for an induction heating device on the other hand. In the present case, this may be relevant only for the expected temperatures or the temperatures to be adjusted regarding the embodiment shown in FIG. 1.
 The heating device 18 is advantageously pressed against the bottom side 14 of the cooktop plate 13 even though it is not directly fixed to it. However, a defined position can thus be achieved.
 An indicator device 20 in a ring shape is arranged around the heating device 18. It runs relatively close to the heating device 18 and can either have a small distance to the bottom side 14 of the cooktop plate 13 or it can abut the latter or be pressed against it. However, actual fastening of the indicator device 20 is effected using separate fastening means. On the one hand, a fastening protrusion 22 can be provided as shown in FIG. 1 (left side) on which the indicator device 20 is mounted, for instance bonded or clamped. The fastening protrusion 22 can be provided on the side of the heating device 18 or rather project from the latter, e.g. formed as a sheet metal connecting link or the like. As an alternative, it can be clamped thereon as a circular ring or the like.
 An alternative embodiment of a fastening protrusion 22' is shown on the right side of FIG. 1, with said fastening protrusion not directly provided on the heating device 18 but either on a separate fastening means which might possibly also support the heating device 18 as well as further heating devices of the cooktop. The fastening protrusion 22' may alternatively also be bonded to the bottom side 14 of the cooktop plate 13 in a non-detachable manner and then, for example by clamping or snapping into place, support the indicator device 20. On the one side, the arrangement of the indicator device 20 around the heating device 18 and in the close vicinity thereof may be important in this case. On the other side, the indicator device 20 can actually be pressed against the bottom side 14 of the cooktop plate 13 and, under certain circumstances, this may even be advantageous. In any case, the indicator device 20 is not fastened to the cooktop plate 13 in a non-detachable manner, for example by adhesive bonding or direct coating. In this way and by means of the present disclosure, the structure or the production of the cooktop plate 13, respectively, may be more simple.
 When operating the heating device 8, there is a differentiation between a radiant heating device or a keep-warm heating device or a contact heating device, respectively on the one hand and an induction coil on the other. In the case of a radiant heating device, the latter is emitting, e.g. by means of glow heating elements in the type of filaments or the like, upwards through the cooktop plates 13 by means of its heating capacity which is then coupled into a vessel or the cooking contents in the vessel, respectively via a bottom side of the cooking vessel which is placed on top of it. Thereby the cooktop plate 13 gets heated directly through the radiated power and indirectly via the bottom part of the vessel. After finishing the cooking process, this is then leading to the problem of said high temperature of the cooktop plates 13 or the upper side 15 thereof in this area, and that is why a heat indicator or residual heat indicator is required in order to protect an operator from accidental contact. Similar is the case of the keep-warm heating device or the contact heating device, respectively, which only heats up the cooktop plate 13 directly by abutting against the latter. The heated cooktop plate 13 passes its heat on to the indicator and can cause the above mentioned color change there at a certain change temperature.
 Assuming an above mentioned crucial temperature of 50° C. to 70° C. or even of up to 90° C. regarding the cooktop plate where a residual heat indicator device should be activated when the temperature is exceeded, said change temperature can be selected even lower in view of the heat transmission from the cooktop plate 13 to the indicator device 20. When operating the heating device 18 in the form of a radiant heating device, the indicator device 20 will indeed be heated to a significantly higher temperature, that is to say 150° C. to 250° C. in practice. However, this does not matter since in this case, the change temperature has been exceeded and the color change is effected at the fluorescent thermochrome paint. In that context, the essential issue is the temperature below said change temperature, and the consequence that an optical indication disappears again or that it should be present until the change temperature is reached, then in the case of higher temperatures. Therefore, a change temperature of 35° C. to 60° C., for example, may be sufficient in this case, particularly also if the indication device 20 is directly fitted to the bottom side 14 of the cooktop plate 13, and thus providing a very good heat transmission at very similar temperatures. Of course, when selecting the change temperature of the thermochrome paint, it must be considered that the cooktop plate 13 may even be hotter in the central area above the heating device 18 than in the border areas close to the indicator device 20.
 The indicator device 20 consists of a carrier 23 which is made from heatresistant plastics or other materials such as Mikanit or ceramics, for example. Fluorescent thermochrome material is applied thereof as a paint 24 or as a powder which is admixed to the paint 24 respectively. In the case of a temperature at the indicator device 20 which lies above said change temperature, the thermochrome paint 24 can change its color from an unremarkable color, such as a dark color like blue, to the fluorescent luminous color such as red, which then serves as a clearly visible indicator or residual heat indicator. In this way, by the color change for temperatures above said change temperature, the optical residual heat indication is generated/formed by the changed fluorescent thermochrome paint itself.
 In case an induction heating device is used as heating device 18, the latter can directly heat up the indicator device 20 only to a minor degree, for example due to losses in an induction coil. Inductive heating of a correspondingly heatable carrier 23 of the indicator device 20 is to be rejected, particularly also because it would then in turn be independent of the temperature of the cooktop plate 13. In this respect, the indicator device 20 having the fluorescent thermochrome paint 24 is only heated by the return heat of the cooktop plate 13 just as already described before. Thereby the induction heating device does not directly heat the cooktop plate 13 but only gets hot because of the return heat of the directly heated bottom side of the vessel, and therefore the cooktop plate is heated less intensively or mainly at lesser rate, respectively.
 An alternative embodiment of the cooktop 111 according to FIG. 2 includes an induction heating device for a heating device 118. Said induction heating device 118 is provided with an indicator device 120 on the upper side thereof and is pressed against the bottom side 114 of a cooktop plate 113 together with said device. Pressing the induction heating device 118 can be effected by conventional ways and means, for example by mounting on a conventional carrier plate (not illustrated) together with other induction heating devices of the cooktop plate 111, with the carrier plate in turn being fastened to fastening means located laterally at the border of the cooktop plate 113. As an alternative to the induction heating device, generally an above mentioned keep-warm heating device or contact heating device may be used which is usually also pressed against the bottom side of the cooktop 111. The heater may include a carrier on which an electrically resistance heating element is provided, optionally having an insulating layer interposed in case of a metal carrier which is made from sheet metal or the like, wherein in FIG. 4, the carrier lies on top, and is pressed directly against the bottom side 114 of the cooktop 111 for heat transfer. An indicator device 120 would in this case be arranged on the upper side of the carrier, while the resistance heating element is provided on the bottom side thereof.
 The large-area indicator device 120 arranged on the upper side of the induction heating device 118 is hence directly pressed against the bottom side 114 of the cooktop plate 113, but it is not directly fastened or bonded to it or otherwise mounted in a non-detachable manner. The specific structure of the indicator device 120 can be seen from FIG. 4. A carrier film 123 has an adhesive label 126 on the bottom side thereof, by means of which it is bonded to the upper side of the induction heating device 118. In this case, the carrier film 123 can also be a so-called Kapton film or another insulating film or insulating plate, for example, as usually placed on the upper sides of induction heating devices for pressing against the bottom side of cooktop plates.
 A paint layer 128 is located on the upper side of the carrier film 123, for example an above mentioned thermochrome paint which, in an advantageous configuration, has a dark color shade such as dark-red in cold state. It can either be provided in a large-area manner, essentially as large as the indicator device 120, or it may have the shape of a symbol, such as the letters "H O T" according to FIG. 3 for example. In this case, it has such properties that it is dark below a change temperature and thus cannot be perceived through the cooktop plate 113. Above said change temperature, the fluorescent thermochrome paint 124 takes on a luminous color, such as luminous red, and is visible in the form of the symbol or writing, respectively according to FIG. 3. In this way, it serves as a residual heat indicator.
 The advantage of the indicator device 120 being arranged directly above the heating device 118 as can be seen in FIG. 2 is that usually, such induction heating devices having induction coils already include an insulating film on the upper side thereof, for example an above-mentioned Kapton film, or alternatively an insulating plate. Thus, additional components are not required, but only components which are designed in a different manner. Said components may then be provided with a printing or an adhesive label depending on the customer's preferences and the application or type series, respectively. Another advantage is that then a large-area residual heat indicator can be achieved which could not be implemented that well by means of the ring-shaped embodiment according to FIG. 1.
 Finally it can be assumed that the maximum residual heat at the cooktop plate 113 is located in the central area centrally above the heating device, and therefore an optical residual heat indicator should consider it. On the one hand, this can be effected by means of known per se temperature distributions ranging from said central area to the lateral border area beyond the outer edge of the heating device 118 in terms of both time and space. Nevertheless, a residual heat indication directly including said central area is more precise. This also speaks in the favour of this embodiment.
 As an alternative to the specific embodiment of the indicator device 120 having a layer of paint 128 and a thermochrome paint 124 applied on top of the latter, two thermochrome paints may also be provided having different color change temperatures, that is to say two different types of powder including thermochrome material. One of them has a change color at a higher temperature, for example corresponding to a temperature on top of the cooktop plate of significantly more than 100° C., that is to say when contact is still very unsafe. The other change temperature may occur at a temperature corresponding to a temperature at the cooktop plate of approximately 50° C. to 70° C., that is to say the usual value for residual heat indicators, where below said temperature contact to the cooktop plate no longer implies burning risks. Said two thermochrome paints may be arranged side by side. The one with the lower change temperature represents the word "H O T" at the bottom according to FIG. 5. The fluorescent thermochrome paint having the higher change temperature can accordingly indicate "V E R Y" in intensive colors correspondingly. In case of a very hot cooktop plate, "V E R Y H O T" will be displayed by the indication device 120, and at slightly lower temperatures but still above the limit temperature of 50° C. to 70° C., only "HOT" is displayed according to FIG. 3
 FIG. 6 shows that also a logo can be indicated instead of a writing. The upper part of FIG. 6 shows how the thermochrome paint layer has a particular unremarkable color shade in the cold state, such as dark blue, for example. In the heated state above the limit temperature of 50° C. to 70° C., the color shade changes, as in the illustration below, and gets luminous blue, for example. This can either be used as a temperature indication for warning purposes or as a temperature-depending operation indicator, so that in the heated state, the logo of the producer of the appliance, for example, appears luminous and is clearly discernable even through a colored cooktop plate. Advantageous and preferable embodiments of the disclosure are the subject of the claims below. The wording of the claims is incorporated into the content of the description by explicit reference.
Patent applications by Wolfgang Thimm, Karlsruhe DE
Patent applications by E.G.O. Elektro-Geratebau GmbH
Patent applications by E.G.O. ELEKTRO-GERÄTEBAU GMBH
Patent applications in class STOVE LIDS AND TOPS
Patent applications in all subclasses STOVE LIDS AND TOPS